Valve train components, such as switchable hydraulic pivot elements, switchable roller lifters and valve lifters, typically comprise an outer housing with a bore therein that houses an inner cylindrical body which moves reciprocally in the bore. The bore and the inner housing are concentric and the surface of the bore and the outer surface of the inner housing have opposing cylindrical surfaces which are coaxial to one another.
In order to prevent rotational movement between the two opposing cylindrical surfaces, anti-rotational mechanisms, such as a channel and a pin, are often used. The channel is cut or formed axially in one of the opposing cylindrical surfaces and a pin is radially fixed in the other opposing cylindrical surface. The pin extends radially into the channel and, thereby, prevents rotational movement between the two cylindrical surfaces. The channel can be closed at one or both ends such that the closed end of the channel acts as a stop to control lash between the outer and inner housings.
It can be difficult to form the channel-pin arrangement in the opposing cylindrical surfaces. The groove has to be cut in one of the opposing cylindrical surfaces, a hole has to be drilled in the other of the opposing cylindrical surfaces, and the pin inserted in the hole. Depending on the size of the two cylindrical members, this can be a rather complicated process.
In switchable valve train components, mechanical lash is generally defined as the axial play or clearance between the locking mechanism of the inner housing and an engageable feature on the outer housing during the locked mode. Control of mechanical lash is achieved by altering the axial height of the locking mechanism contained within the inner housing with respect to the engageable locking surface of the outer housing.
It is important to control mechanical lash to a specified range and avoid excessive play or movement between the inner and outer housings. The camshaft that actuates a switchable component is designed to accommodate the prescribed mechanical lash. If the mechanical lash falls outside of the design parameters of the camshaft, the potential for accelerated locking mechanism wear is increased. In this state, the dynamic performance of the valve train may be compromised. A controlled mechanical lash between the housings provides for a more durable switchable valve train component as well as the other components of the valve train.